This invention is in the technical field of nuclear magnetic resonance (NMR) measurements. More particularly, the invention relates to a method and apparatus for controlling temperature of liquid samples before and during an NMR measurement in an NMR spectrometer.
In high throughput NMR techniques, saving time is of paramount importance. Most high throughput NMR techniques use a flow probe, and a liquid sample is pushed into the NMR probe through a tubing with a small inner diameter to an active region, or a flow cell of the probe. Thereafter, precious time is lost in heating the sample to thermal equilibrium. The time to reach thermal equilibrium in a currently used NMR probe of a prior art design may be two minutes or longer, depending upon the desired end temperature.
It is a general object of this invention to improve the throughput time in NMR measurements.
It is a particular object of this invention to provide a method and apparatus for preheating a liquid sample being pushed into an NMR probe without disturbing the magnetic field for the measurement.
For carrying out an NMR experiment according to the present invention, the inlet tubing through which a sample liquid flows from a sample source into a flow cell is provided with a heater comprising a twisted-pair wire tightly wrapped around helically such that the sample liquid is preheated as it flows into the flow cell and hence that the time taken for it to reach thermal equilibrium is reduced. The use of a twisted-pair wire as a heater minimizes the effect of induced magnetic field. A process control device, commercially available, may be used to monitor and control the temperature of the inlet tubing and thereby controlling the electric current through the heater such that the temperature can be maintained at a desired level.